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A New Method for Measuring Plant Available Water Capacity Helps Document Benefits of Biochar-Soil Mixtures

This is part of a series highlighting work by Washington State University (WSU) researchers through the Waste to Fuels Technology Partnership between the Department of Ecology and WSU during the 2017-2019 biennium.

Assorted apparatus used to measure plant-available water holding capacities.
Figure 1. Apparatus used to measure plant-available water holding capacities (PAWC) by conventional and centrifuge methods. A) pressure-plate apparatus for conventional field capacity measurements, B) soils in cups on top of pressure membrane, C) dew-point psychrometer for conventional wilting-point measurements, D) assembled centrifuge filter tube showing removable filter top containing soil to right, and E) rack containing large number of assembled and loaded centrifuge tubes. Source: Amonette et al., 2019.

Biochar has potential to draw down atmospheric carbon when applied to agricultural soils (as discussed in my previous article on this topic). There is currently not a robust way for farmers to be directly compensated for the benefits to society such drawdown provides. However, researchers have been exploring other co-benefits of using biochar as a soil amendment. One such co-benefit is biochar’s ability to increase the water-holding capacity of agricultural soils, and thus increase plant productivity in situations where water is limiting. However, documenting this effect has been limited by how time consuming and expensive it is to measure plant-available water-holding capacity (PAWC) by standard methods (See Figure 1 A, B, C). In an effort to alleviate this barrier, Jim Amonette at the Pacific Northwest National Laboratory and Washington State University’s Center for Sustaining Agriculture and Natural Resources led the development of a new, inexpensive, rapid method for measuring PAWC of soil-biochar mixtures (See Figure 1 D, E), based on applying a specific level of water potential to a sample using a centrifuge. The sample is supported by a filter membrane fixed midway in a centrifuge tube, thus allowing drainage into the bottom of the tube to occur.

Figure of soil texture triangle.
Figure 2. Soil textural triangle showing textural distribution of Washington A horizons in the USDA National Cooperative Soil Survey database (gray dots), and the nine natural Washington soils and one synthetic soil (borosilicate glass beads) used in this work (blue and yellow squares). Source: Amonette et al., 2019.

The new method was calibrated against standard methods and then applied to 72 combinations of soil and biochar: nine Washington soils of varying textures (Figure 2), each combined with four biochars, and at two different biochar application rates. Use of this new, rapid method for measuring PAWC allowed Amonette’s team to collect data in just five days, when use of standard methods would have taken several months. This new method therefore has great application potential as a screening tool in future research and in monitoring changes in PAWC over time.

The data collected from the 72 combinations of soil and biochar led to the following conclusions regarding the effects of biochar amendments on the PAWC of soils:

  1. Biochar did increase the PAWC of soils, though the increase in PAWC was not linearly proportional to the amount of biochar added. The addition of 0.5% and 2.0% biochar carbon (by weight) increased PAWC by 2.7 and 3.3%, respectively, averaged across all biochar-soil combinations. These application rates are approximately equal to biochar amendment rates of 5 and 20 tons of carbon per acre when mixed to the 15-cm plow depth. In other words, 80% of the maximum PAWC benefit observed was obtained with addition of only 0.5% biochar carbon; applying four times as much carbon did not yield a proportional increase in terms of PAWC (Figure 3).

    Figure showing mean increase in PAWC for 9 WA soils.
    Figure 3. Mean increase in PAWC for nine Washington soils observed using the centrifuge method and expressed as a function of the nominal rate of biochar application per acre assuming 1 acre of soil 6 inches deep weighs 1000 tons. Error bars represent 1 standard deviation. Least significant difference (P < 0.05) in PAWC increase between the two addition rates for a given soil is 0.18%.
  2. Soil texture and mineralogy have a large impact on the degree to which biochar increases PAWC (Figure 4), with sandy soils, in general, receiving proportionally greater benefit from the higher biochar application; and

    Bar graph showing mean changes in PAWC
    Figure 4. Mean changes in plant-available water-holding capacity (PAWC) as a function of soil type (as shown in Figure 2) and biochar amendment rate. Error bars represent 1 standard deviation. Different letters above error bars indicate significant (P=0.05) differences among means. Means having error bars without letters are not significantly different from means labeled with a, b, or c. LSD (least significant difference) = 0.78 weight %. Source: Amonette et al., 2019.
  3. Inter-particle effects (caused by interactions between biochar and soil particles) are the largest contributor to the overall impact of biochar on PAWC. The exact mechanisms at play were not part of this study but could include creation of new void spaces between biochar and soil particles or increasing the proportion of hydrophilic to hydrophobic surfaces in the biochar-soil mixture. Amonette and his colleagues found that the increase in PAWC in soil-biochar mixtures could not be explained by the internal porosity of biochar alone, but instead was explained by the interaction of biochar and soil particles. Averaged across soil-biochar combinations, 86% and 62% of change in PAWC was attributable to these inter-particle effects for the 0.5% and 2.0% biochar application rates, respectively.

One important take home message is that biochar benefits do not necessarily increase proportionally with application rate. Figuring out the particular “sweet spot” to achieve the most economical application rate will be specific to a particular soil-biochar-crop combination. The dominance of the inter-particle effects in PAWC increases in this study was fascinating and begs for more research. This and future work will get us closer to what is considered the holy grail of biochar application: being able to target a particular biochar to a particular soil type to solve a particular issue – in this case, improving water-holding capacity.

For more detail, see the brief project report (13 pages, Chapter 8 in Hills et al. 2019) or the longer technical report (Amonette et al., 2019: 35 pages).


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Just-In-Time Soil Health

How much is enough soil organic matter? “The more, the better” is often the assumed answer, or at least as much as the native soil had before crops were grown. There are a few papers on the topic (Loveland and Webb, 2003), some recent (Schjønning et al., 2018 and Oldfield et al. 2020) But is this the right question?

Janzen (2006) wrote, “organic matter is most beneficial, biologically, as it dissipates by microbial activity…”

So, the flow of organic matter derived energy through the soil is at least as important as how much is stored as organic matter, I thought.

Organic matter is like stored inventory, in a warehouse.

I’ve read that maintaining warehouse inventory is expensive.

Is it expensive in the soil? Yes, it is difficult to increase and difficult to maintain high levels in annual cropping systems.

What did I learn back in high school about just-in-time management…?

Just-In-Time Soil Health

I am not generally interested in business concepts, but for some reason the idea of just-in-time production intrigued me from when I first heard of it back in the 1980s. “The process involves ordering and receiving inventory for production and customer sales only as it is needed to produce goods…” The supply of parts or materials is delivered Just-In-Time to the manufacturing process on an as-needed basis. Toyota is famous for starting the concept. It allows businesses that make something, like Toyota, to keep their inventory low and warehouses smaller and so to cut costs. But it requires accurate forecasts of demand, reliable suppliers, synchronizing supply with demand, quick delivery of supplies, and maintaining a steady production rate.

Could it apply to soil management? Janzen is a researcher in Canada whose thinking about soil carbon cycling focuses on carbon’s flow through the soil; “organic carbon may be best viewed, not as a reservoir entrapped in soil, but as a stream of atoms flowing through.” (Janzen, 2015)

At risk of being accused of being a reductionista, I am going to compare the soil to a factory. And although I do not usually go for conjecture, that is what much of this is. Nevertheless, think about it; the parts and materials of the soil are photosynthesis-produced carbon, really the energy, in the soil. Soil organic matter is the soil’s warehoused inventory of this energy with particulate organic matter in a nearby warehouse, and therefore more available for use, while the mineral-associated organic matter warehouse is further away, less available. And just as with a factory, it is difficult/expensive to maintain a high level of this inventory in the soil.

The soil’s product is microbial life and all the functions it provides. This microbial life is dependent on the flow of photosynthetic energy from plants. “Plant input fuels the whole system and drives the microbial pump,” (Kastner and Miltner 2018). If it could be done, we would want the benefits of the energy flow through the soil but without the need to build and maintain a massive warehouse full of organic matter; we want Just-In-Time soil health.

Here is how it could work: 1) If we provide enough just-in-time energy we will 2) attain desired soil function, and 3) reduce the need to maintain high inventories of soil organic matter. The key to this, just as in a factory, is an accurate forecast of the demand: when is it needed and how much? Demand here is the flow of photosynthesis-derived C-energy through the soil needed to provide the desired function. Then we need to be able to provide enough energy at the time it is needed, just-in-time.

Demand can be either productive or unproductive. Productive energy demand goes to soil biological function, maintaining soil structure, suppressing soilborne pests making nutrients available, etc. Unproductive demand is from tillage looting our soil warehouses for some short-term gain but at great expense in lost inventory. Unlike a factory, we cannot be very exact about demand and energy flow rates in the soil, but we can make educated guesses about when extra just-in-time flow would be useful and how we might provide such a flow.

When is demand high and how might this be managed in a soil? The period of crop stand establishment is crucial for the rest of the growing season. Seeds germinate, roots grow, shoots emerge. However, cooler soil temperatures and lack of living plants can limit the energy flow from decomposition of our warehoused soil organic matter. This is when we should attempt to insure a good flow of C-energy through the soil.

How can we provide this just-in-time flow? Planting green, including a carbon source with fertilizer, C-containing seed treatments, some relay crops, some cover crops, green manures, manure, and compost applications. Not every use of these practices is a JIT example, but they all can be.

(Left) Two tractors tow planting hoppers through a field; (Right) Compost pellets on graph paper
The idea behind planting green (above left), molasses-based amendments or pelleted compost (above right) applied at planting, and similar short-term interventions is a just-in-time bump in the carbon/energy flow through the soil.

(Planting green photo by Michael Strang, Pelleted compost photo by Thad Schutt, Compell, both used with permission)

Consider the use of mustard green manures here in the Columbia Basin of Washington state. A late fall incorporated green manure crop can produce JIT flow to an early planted potato crop the next spring. It starts with a large amount of green, easily decomposed biomass incorporated into cooling soils, which slows the resulting burst of microbial growth, perhaps just enough to make it effective for potato seedlings when the soil begins to warm the next spring. The resulting flow improves water infiltration and resistance to wind erosion and provides some soilborne pest suppression in low organic matter soils. Although the effects are not long term, they are often enough for the following spring’s potato crop to become established and close canopy before dissipating.

Location is important for the JIT soil health. Seed treatments and furrow applications will be most likely to affect seeding growth. Pelleted compost applied in the seed furrow is being tested. This would ensure needed flow at the right locations for growing seedlings. The 4R’s of nutrient management apply here too; right material, rate, time, and location.

These and other similar Just-In-Time soil health management strategies are being recommended at some grower meetings. Some, like cover crops and green manures, have been the focus of research but many others have not. I found a few published papers (if you know of more, please mention them in the comments). An early foray into this strategy was undertaken by Ritz et al. (1992). They observed the effects of N fertilization of potatoes with and without C as straw or sugar (sucrose). Combining N+sucrose provided increased microbial biomass for up to 25 days after incorporation, enough time for the seedlings to get established.

In a lab experiment with field soils (Stenstrom et al. 2006), addition of glucose induced a quick transition from dormant to active microbial states that lasted at least 27 days.

There are other studies, but not many. In their review, Managing Soil Microorganisms to Improve Productivity, Welbaum et al. (2004) have a section on JIT strategies which they call Feeding Soil Microbes, mainly using sugars. It provides an informative discussion of the few published research results but highlights the need for more research in this area.

Once established, photosynthesis in seedlings can begin to produce their own flow of energy to the soil through root exudates. Soil energy flow for the rest of the season is provided through these exudates and from organic matter.

Hand draw graph showing Carbon/Energy Flow through Soil across seasons.
An idealized conception of Carbon/Energy flow from various sources through a cropped soil.

1Technically this is rhizodeposition which includes exudates and sloughed off cells. Total flow quantities crops ranges from 0.3x to 1x that from the decay of soil organic matter which varies by decay rates (1-5% of total SOM annually). Flow from annual crop roots increases rapidly for a few months and then declines (Pausch & Kuzyakov, 2018).
2 Just-in-time flow is much smaller than other flows but comes at a critical time for the crop and when other flows are lower because of low soil temperature. It is also often concentrated at or near the germinating seed.

Just like with JIT manufacturing, there are risks for this soil management strategy. If the energy flow to the soil is early or late or broken, the benefits are missed. If the demand is higher than anticipated or more than our chosen practice can supply, the benefits are missed. This is where the Just-In-Case management comes in.

Just-in-Case Soil Health

The storage organic matter should not be neglected as it provides a base flow of energy in the soil. In the business comparison, this is the Just-In-Case inventory.

There is nearly always a flow of energy coming from the decay of your soil’s organic matter, organic amendments, and dead plant roots and shoots. Its rate varies by the amount of these materials present and the temperature and water status of the soil. We can increase this flow by building up inventory levels Just-in-Case something goes wrong. Higher soil organic matter levels can keep the base flow rate at a higher level, reducing risk of low supply at the wrong time, but there is always a cost to doing this. Just as in a factory, there is a trade-off between the risks of just-in-time management and costs of just-in-case management.

Just-in-Case Management Just-in-Time Management
Qualities Source or Practice Source or Practice Qualities
  • Base flow
  • Slow acting
  • Continual flow
  • Large quantity
  • Dispersed in soil
Soil organic matter decay
  • Supplementary flow
  • Fast-acting
  • Short-term flow
  • Small quantity
  • Precise location
Broadcast manure and compost Liquid manure
Pelleted compost
Crop biomass Molasses and other sugar-based products
Cover crop biomass Green manures
Crop root exudates Relay crops
Cover crop exudates Planting green

How much is enough?

As with soil organic matter, we would like to know how much energy flow in the soil at the critical times is enough. One problem here is measurement of that flow; we don’t have an accurate way of doing it. It can be imperfectly measured with active carbon tests (POXC) and soil respiration-related tests like the Solvita. However, these provide only snapshots of the flow and so should be measured regularly, or at the critical times for your crop growth.

Finally, a reminder that I have indulged in speculation here. Although the mechanism behind just-in-time interventions seems reasonable, whether they can consistently make a difference in yield, or crop health, or in input reduction remains to be seen. The determining factors will be soil organic matter levels, soil temperature and water, and crop stage. For now, I think both just-in-time and just-in-case strategies—carbon-energy flow and soil organic matter—should be part of soil health management.

What about the piece I had planned to write: how much soil organic matter is enough? That is a complicated question and will have to wait for a future blog post.


  • Janzen, H.H. 2006. The soil carbon dilemma: Shall we hoard it or use it? Soil Biology and Biochemistry 38(3): 419–424. doi: 10.1016/j.soilbio.2005.10.008.Janzen, H.H. 2015. Beyond carbon sequestration: soil as conduit of solar energy. European Journal of Soil Science 66(1): 19–32. doi: 10.1111/ejss.12194.
  • Kästner, M., and A. Miltner. 2018. SOM and Microbes—What Is Left from Microbial Life. In: Garcia, C., Nannipieri, P., and Hernandez, T., editors, The Future of Soil Carbon. Academic Press. p. 125–163
  • Loveland, P., and J. Webb. 2003. Is there a critical level of organic matter in the agricultural soils of temperate regions: a review. Soil & tillage research 70(1): 1–18.
  • Oldfield, E.E., S.A. Wood, and M.A. Bradford. 2020. Direct evidence using a controlled greenhouse study for threshold effects of soil organic matter on crop growth. Ecological Applications n/a(n/a). doi: 10.1002/eap.2073.
  • Pausch, J., & Kuzyakov, Y. (2018). Carbon input by roots into the soil: Quantification of rhizodeposition from root to ecosystem scale. Global Change Biology, 24(1), 1–12.
  • Ritz, K., B.S. Griffiths, and R.E. Wheatley. 1992. Soil microbial biomass and activity under a potato crop fertilised with N with and without C. Biol Fertil Soils 12(4): 265–271. doi: 10.1007/BF00336042.
  • Schjønning, P., J.L. Jensen, S. Bruun, L.S. Jensen, B.T. Christensen, et al. 2018. The role of soil organic matter for maintaining crop yields: Evidence for a renewed conceptual basis. Advances in Agronomy. Elsevier. p. 35–79
  • Stenström, J., K. Svensson, and M. Johansson. 2001. Reversible transition between active and dormant microbial states in soil. FEMS Microbiol Ecol 36(2–3): 93–104. doi: 10.1111/j.1574-6941.2001.tb00829.x.
  • Welbaum, G.E., A.V. Sturz, Z. Dong, and J. Nowak. 2004. Managing Soil Microorganisms to Improve Productivity of Agro-Ecosystems. Critical Reviews in Plant Sciences 23(2): 175–193. doi: 10.1080/07352680490433295.

2019 Annual Report Available

CSANR’s 2019 annual report is now available, and we encourage you to check out some of the great things going on! The report can be accessed on our Mission page. We’ll also be posting some of the material from the annual report on our blog in the coming weeks and months.

Check it Out: Can Biochar Be Used for Carbon Dioxide Drawdown in Washington State?

Tarp bag filled with biochar
Figure 1. Biochar has the potential to improve agricultural soils and sequester carbon. Source: USDAgov, licensed under CC PDM 1.0.

This is part of a series highlighting work by Washington State University (WSU) researchers through the Waste to Fuels Technology Partnership between the Department of Ecology and WSU during the 2017-2019 biennium.

In a recent study, Jim Amonette at the Pacific Northwest National Laboratory and Washington State University Center for Sustaining Agriculture and Natural Resources developed an improved method to estimate the technical potential for biochar (Figure 1)—made from forestry residues and waste wood (Figure 2) and applied to agricultural soils in Washington State—to store carbon, drawing down atmospheric carbon (C) and contributing to mitigating climate change. Amonette selected twenty-six counties in Washington State for application of this improved method (Figure 3). For each county, Amonette developed seven biomass feedstock and biochar process scenarios including one for waste wood harvested from municipal solid waste alone, and six for waste wood combined with forestry residues from timber harvesting operations. The research generated results for each of the 26 counties.

Waste wood burns in oil tank repurposed as a kiln.
Figure 2. Biochar can be produced in commercial facilities or by using kilns like this oil tank kiln close to the source of waste wood. Photo: Wilson Biochar Associates; used with permission.

For the 26 counties studied over a period of 100 years, biochar could store between 8 and 411 million metric tons of biochar C, resulting in an immediate offset of between 11 and 354 metric tons of C. These values decrease by 50% if the same sustainably procured biomass were instead combusted for renewable energy. The analysis shows that biochar-C storage capacity is lowest for counties that generate large amounts of woody biomass, and consequently, after a few decades they will need to export their biochar to agricultural counties, located primarily in the southeast quadrant of the state. However, under current storage potential assumptions, the 26-county biochar-C soil storage capacity will be saturated in 54 to 109 years for the scenarios that include timber harvest biomass residues. Amonette added that the development of additional storage technologies and reservoirs such as forest and rangeland soils would allow this limit to be pushed to higher levels.

Map of Washington counties with colored dots representing study rankings..
Figure 3. Dots on the map show the 26 counties selected for this study based on their ranking in four categories relevant to biochar production or use potential: Municipal Solid Waste (pink), Forest Biomass (blue), wildland urban interface Fire Risk (red), and Agricultural Productivity (orange). For explanations of categories and names of counties, see Amonette, 2019. Source: Amonette, 2019.

For more detail, see the brief project report (12 pages, Chapter 6 in Hills et al. 2019) or the longer technical report (Amonette, 2019: 174 pages).


  • Amonette, JE. 2018. Assessing local technical potentials for CO2 drawdown using biochar from forestry residues and waste wood in Washington State. p. 271-293 (Chpt. 14) in Advancing Organics Management in Washington State: The Waste to Fuels Technology Partnership 2015-2017 Biennium. Washington State Department of Ecology Publication Number 18-07-010.
  • Amonette, J.E. 2019. Assessment of the Local Technical Potential for CO2 Drawdown using Biochar from Forestry Residues and Waste Wood in 26 Counties of Washington State A technical report completed as part of the Waste to Fuels Technology Partnership. 174 pp.
  • Hills, K., M. Garcia-Perez, J.E. Amonette, M. Brady, T. Jobson, D. Collins, D. Gang, E. Bronstad, M. Flury, S. Seefeldt, C.O. Stöckle, M. Ayiania, A. Berim, W. Hoashi-Erhardt, N. Khosravi, S. Haghighi Mood, R. Nelson, Y.J. Milan, N. Pickering, N. Stacey, A.H. Tanzil, J. Zhang, B. Saari, and G. Yorgey. Advancing Organics Management in Washington State: The Waste to Fuels Technology Partnership, 2017-2019 Biennium. 2019. Publication 19-07-027. Solid Waste Management Program, Washington Department of Ecology, Olympia, WA.
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Postponed: Register now to attend Digital Ag-athon 2020

Due to the evolving situation surrounding the nationwide COVID-19 outbreak, this event has been postponed. New dates will be selected and announced when normal operations have been restored. Thank you.

In partnership with Microsoft and Innov8ag, we are hosting Digital Ag-athon 2020—the first agriculture-focused hackathon at WSU. The event is currently open to WSU affiliates only. Students, postdocs, and researchers from all backgrounds and all WSU campuses are welcome to participate. We also have limited travel support for participants from non-Pullman WSU campuses.


Digital Ag-athon 2020—the first agriculture-focused hackathon at WSU


WSU affiliates.

  • WSU students, postdocs, and researchers from all backgrounds and all campuses.
  • Limited travel support available.


April 2-3, 2020 (all day)


PACCAR building, Pullman campus. Some travel support available for participants from non Pullman Campuses.


Learn new skills, make new friends, and have a great time. Use cloud computing, the Microsoft Azure platform, satellite and other imagery to deliver agriculture-focused insights.

Register Online

Register online now:

Seats are limited. So please register ASAP. Once you register, you will hear more from us on specifics and details.

WSU Sponsors

  • College of Agricultural, Human, and Natural Resource Sciences
  • Voiland College of Engineering and Architecture
  • Office of Research Advancement and Partnership
  • Department of Biological Systems Engineering
  • Center for Sustaining Agriculture and Natural Resources

Thank you and hope to see everyone at Digital Ag-athon 2020!

Download a shareable flyer

Position Announcement: Post-Doctoral Associate/Research Associate (Pullman, WA)

Washington State University’s Agricultural, Natural, and Human Systems Modeling group seeks applications for a post-doctoral associate (or a qualified post-masters research associate) with broad interests in facilitating decision support at the intersection of climate, agriculture and natural resources issues in the Pacific Northwest U.S. The position will be based in Pullman, WA with the Department of Biological Systems Engineering and will work in affiliation with the Center for Sustaining Agriculture and Natural Resources as well. It offers the opportunity to work in a trans-disciplinary environment with intellectual engagement from colleagues with diverse backgrounds in Research, Extension, and Decision Support.

Position Description (pdf)

Review of applications will start February 2020. The position will remain open until filled. Contact Kirti Rajagopalan ( for additional information.

How does regenerative agriculture reduce nutrient inputs?

“When you start farming regeneratively, you rely a lot less on external inputs, such as fertilizers…”  – Tom Tolputt

One of regenerative agriculture’s extraordinary claims is that it can drastically reduce or even eliminate nutrient inputs, fertilizers. How is this possible? The go-to explanation is often “soil biology” – revved up soil biology makes nutrients available that plants can’t normally access. As it often the case, there is a bit of truth here. Regenerative ag can reduce inputs, and soil biology is involved along with other natural processes, but the whole truth may be much more ordinary.

Reduce exports to reduce inputs

Cattle graze in snowy field.
Livestock grazing is the source of regenerative agriculture’s reduction in nutrient input needs. (Photo by Andrew McGuire, WSU)

The key principle of most definitions of regenerative agriculture is the integration of livestock into cropping systems. The grazed livestock component of regenerative agriculture allows for several advantages that annual cropping cannot give including improved soil health. It also reduces the need for nutrient inputs though a series of system changes that start with reduced exports.

Consider the export of nutrients from a grazed pasture vs. a harvested crop. Whitehead (2000) estimates the yearly nitrogen removal in the beef produced on a moderately-intensive grazed pasture1 at 22 lb./ac. Similarly small amounts of P, 2 lb./ac, and of the rest of the important soil nutrients are removed. Compare this to the 134 lb. of N and 27 lb. of P removed per acre  in an average 180 bu/ac corn crop (Ohio State Extension); the switch from a harvested crop to beef production reduces the export of N by 84% and P by 92%. This reduction in export means that these nutrients do not have to be replaced in the system. Here is the mechanism for the largest reduction of nutrient inputs in regenerative agriculture; it drastically reduces exports.

Reduce cropping intensity; The time factor

Interacting with this reduction in exported nutrients is the longer time that grazing allows the soil to be undisturbed compared to annual crops, even those under no-till. This time allows for greater buildup of nutrients through the natural processes, especially of biologically fixed nitrogen in association with legumes in annual cover crops or perennial pastures.

A short 60-90-day cover crop of mixed cereal-legume species grown in the non-cropped beginning or end growing-season-window fixes a limited amount of nitrogen. However, including livestock grazing provides a financial return that enables a cover crop to be left in the field for much longer than a normal cover crop, even for growing the cover as a substitute cash crop during the main growing season. These are not so much cover crops as they are annual forage crops, and managed as such, the included legumes can fix significantly more N than an ungrazed cover crop.

Close-up of stalks of wheat.
Crops like this perennial wheat may someday help to reduce nutrient losses from fields. (Photo by Eric Sorensen, WSU)

Grazing perennial pasture is even better for nutrient cycling. A perennial grass-legume pasture can fix a significant amount of N over a year or two, easily enough to replace the N being removed in the system. In fact, using the same study as above (Whitehead, 2000), the system is gaining 50 lb./ac of nitrogen every year without any N-fertilizer inputs. Most of the N in the grazed herbage is recycled to the soil through manure and urine which is much more efficient at conserving nutrients than annual cropping systems.

The additional time also gives soil microbiology opportunity to work on the legacy P (Sharpley et al., 2013). It’s called legacy P because it was originally applied as fertilizer but has become mostly unavailable to plants. It is “slowly exchangeable” (van der Bom et al., 2019), and therefore more available than P in or on soil minerals. Microbes, root exudates, and biofertilizers can all play a part in solubilizing this P to make it available for plants (Menezes-Blackburn et al., 2018).

This Strategic Phosphorus Reserve exists to some extent in all our farmed soils that have a history of fertilizer P applications. The more time this process has to work without P removal, the more quantity of P will be available. One recent paper (Menezes-Blackburn et al., 2018) estimates that legacy P could supply P for the next 100 years, not necessarily at a rate sufficient for high yield annual cropping, but certainly more than enough for a beef grazing system. However, while we should draw down levels of legacy P, this is not a natural source of the nutrient and will not last forever.

Another way that nutrient inputs are reduced with the integration of livestock grazing is by having active plants growing year-round (a soil health principle), especially deep-rooted perennial species as is common with grazing systems. This reduces losses of nutrients from leaching and tightens nutrient cycling.

How much does actual soil weathering, the release of nutrients from the mineral portion of the soil, contribute? Release rates may be higher than previously thought, (Bormann et al., 1998), and active soil biology does play a role here, increasing the rates of nutrient release. However, estimated rates remain much lower than the other mechanisms mentioned above, and far too low to support moderate yields of annual crops.

Essentially what regenerative ag is doing with livestock grazing is reducing cropping intensity and therefore yield intensity, substituting production of meat and milk as a trade-off for crop export. If exports are reduced to the point where the soil’s internal ability to provide N, P, and K and other needed nutrients is able to replace all the nutrients removed, then yes, we can have a system where no external nutrient inputs are needed.

Why grow crops at all?

Given all this, why not just skip the crop production altogether? Indeed, many regenerative agriculture practitioners do this, and nutrient inputs are drastically reduced or eliminated. They produce meat, eggs, milk, but no crops. This is great for their soil, and sometimes for grower profits. We can do with less feed and biofuel crops; if these are the crops being replaced by grazing, there is no downside other than the reduced meat production per acre (compared to exported feed crop systems), which is perhaps offset by more sustainably produced meat. Some growers, however, can’t or don’t want to raise livestock.

Can inputs be reduced without livestock integration?

Livestock and cropping have long been separated in most of our modern agriculture. It is not always easy or feasible to integrate them. What is the potential to reduce inputs but only grow crops? There are many opportunities to improve the nutrient use efficiency of annual cropping; more diverse crop rotations, rotations that include legumes, perennials and cover crops, fertilizer formulation and management, combining organic soil amendments with synthetic fertilizers, etc.; and all of these can reduce the need for nutrient inputs (Drinkwater et al., 2017). These systems can also take advantage of the legacy P. Low-input systems using a combination of these methods can drastically reduce nutrient inputs by improving the cycling of nutrients within the system. There is often a modest yield decrease that accompanies these changes, with optimal rather than maximum yields the goal. An all-crop system can be sustained without external inputs of nitrogen (Drinkwater 1998), although other inputs of other nutrients may be needed. When done within a no-till system, it fits within regenerative ag IF regenerative agriculture can be done without livestock, a topic for debate.

Scientists grills a steak while other researchers perform analysis in background.
A regenerative steak, yes, but can we grow a regenerative potato to go along with it? (Photo by Paul Pierlott, USDA ARS)

Non-grain food crops are even less regenerative than annual cereal, biofuel, or feed crops. Consider that a 32 ton/ac russet potato crop here in the Columbia Basin of WA will remove 282 lb. N, 38 lb. P, 311 lb. K per acre plus micronutrients from the field. That would take a whole lot of grazing time to replace without inputs.

What I have not addressed are those regenerative annual cropping systems that do not integrate livestock yet claim to have drastically reduced or eliminated nutrient inputs. Other than the processes already mentioned, I have no explanation for those claims. However, I did find one published example of a cropping-only system that could potentially eliminate all external nutrient inputs. Crews (2005) using a perennial crop system speculates that relying on what he calls “endogenous nutrient supply” (no external nutrient inputs) might just be possible with if the following factors are all aligned:

  • Perennial grain crops are successfully developed and used exclusively.
  • Timing of N release from soil (legumes, bacteria, etc.) must match uptake timing of crop.
  • Crops grown on young to middle-aged soil.
  • A climate favorable for weathering reactions; moderate temperature and precipitation.
  • Exported yields lower than today’s high yields, perhaps much lower.

Such a system could theoretically continue for many decades without nutrient inputs (Glover et al., 2010). This would be the ultimate in regenerative agriculture, but we are not there yet. Some think we may never get there without major concessions in yield (Denison, 2012).

A Beneficial Tradeoff?

This brings us to the inevitable tradeoffs we face in agriculture. There is a basic tradeoff between crop yield and inputs.  Because of the economics, this tradeoff will most likely take place in lower value annual crops (feed, biofuel, etc.) and not in staple, vegetable, or fruit crops. If this is the case, it can be a good strategy for farmers and the soil. For the individual farmer, increased profits may tip the scales in favor of reduced yield and reduced inputs, or increased soil health but less yield. Farmers should do what they need to do to stay in business. However, regenerative agriculture in this form may not be a good strategy for reducing inputs in staple food-crop production, at least not until our population stops growing.

Yes, regenerative agriculture does reduce inputs, but the primary mechanism by which it does this is the reduction of nutrient exports from the field. All the other factors; soil biology, mycorrhizal fungi, diversity effects (other than including legumes), and mineral weathering, are minor factors.

1While regenerative agriculture practitioners generally use intensive grazing, they do not fall into the intensive input use, so these estimates for moderate intensity grazing are probably more accurate than those for intensive systems which add a lot of inputs. Also, there are many factors that affect nutrient flows in grazing systems, so these numbers are only used for example and should not be considered to represent any generalized system.


Bormann, B.T., D. Wang, M.C. Snyder, F.H. Bormann, G. Benoit, et al. 1998. Rapid, plant-induced weathering in an aggrading experimental ecosystem. Biogeochemistry 43(2): 129–155. doi: 10.1023/A:1006065620344.

Crews, T.E. 2005. Perennial crops and endogenous nutrient supplies. Renewable Agriculture and Food Systems 20(1): 25–37. doi: 10.1079/RAF200497.

Denison, R.F. 2012. Darwinian Agriculture: How Understanding Evolution Can Improve Agriculture. Princeton University Press.

Drinkwater, L.E., M. Schipanski, S. Snapp, and L.E. Jackson. 2017. Chapter 7 – Ecologically Based Nutrient Management. In: Snapp, S. and Pound, B., editors, Agricultural Systems (Second Edition). Academic Press, San Diego. p. 203–257

Drinkwater, L.E., P. Wagoner, and M. Sarrantonio. 1998. Legume-based cropping systems have reduced carbon and nitrogen losses. Nature 396(6708): 262–265. doi: 10.1038/24376.

Glover, J.D., S.W. Culman, S.T. DuPont, W. Broussard, L. Young, et al. 2010. Harvested perennial grasslands provide ecological benchmarks for agricultural sustainability. Agriculture, Ecosystems & Environment 137(1): 3–12. doi: 10.1016/j.agee.2009.11.001.

Menezes-Blackburn, D., C. Giles, T. Darch, T.S. George, M. Blackwell, et al. 2018. Opportunities for mobilizing recalcitrant phosphorus from agricultural soils: a review. Plant Soil 427(1): 5–16. doi: 10.1007/s11104-017-3362-2.

Sharpley, A., H.P. Jarvie, A. Buda, L. May, B. Spears, et al. 2013. Phosphorus Legacy: Overcoming the Effects of Past Management Practices to Mitigate Future Water Quality Impairment. Journal of Environmental Quality 42(5): 1308–1326. doi: 10.2134/jeq2013.03.0098.

van der Bom, F.J.T., T.I. McLaren, A.L. Doolette, J. Magid, E. Frossard, et al. 2019. Influence of long-term phosphorus fertilisation history on the availability and chemical nature of soil phosphorus. Geoderma 355: 113909. doi: 10.1016/j.geoderma.2019.113909.

Whitehead, D.C. 2000. Nutrient Elements in Grassland: Soil-plant-animal Relationships. CABI.

No-Regrets Strategies that Benefit Ranching Operations and Provide Climate Resilience

Ranchers already manage multiple risks—including those related to economics, production, the environment, and weather. Climate change represents an added risk, but one that is challenging to manage because impacts are uncertain, variable over space and time, and often perceived as being only of concern in the distant future (Leiserowitz et al. 2011).

Cattle grazing on grassland; mountains in the distance.
Cattle grazing is the main productive activity in the high desert and dry forest landscape of the Bear Valley, near Seneca, Oregon, where our most recent resilience case study is focused. Photo: Jack and Teresa Southworth.

However, despite this challenge, there is a growing recognition that the same strategies that make ranches and rangelands more resilient to climate change will also provide other important co-benefits. These include enhanced resilience to current weather-related variability, enhanced ecological functioning, and in at least some cases, enhanced or more sustainable economic performance.

Implementing these “no-regrets” strategies is thus important for enhancing the resilience of rangelands to a wide variety of shocks including, but not limited to, climate change. Specific strategies include:

  • Management-intensive grazing or other strategies to ensure adequate rest periods. For example, relatively short rotations that ensure that native grasses are allowed to set seed in some years.
  • Regeneration and recovery of degraded plant communities by actively managing grazing. The intent is to manage cattle in a way that the plants’ phenological stage when they are grazed, the duration of each pasture’s use, and the multi-year sequencing of grazing events are selected to promote tillering, seed production, seed-to-soil contact, litter deposition, seed germination, and seedling establishment.
  • Grazing management that increases soil water holding capacity, reduce evaporation from the soil surface, and moderates soil temperatures.
  • Management to reduce fire risk through promotion of native perennial plants and suppression of seed production and establishment of invasive annual grasses.
  • Early de-stocking in the face of drought, to limit over-grazing and economic losses.

The Adaptation Library, created through four years of workshops with rangeland managers and public lands stakeholders around the western U.S., is one resource with a variety of additional ideas for building resilience to climate change for specific regions and vegetation types.

Older man in light-colored cowboy hat and sunglasses.
Rancher Jack Southworth runs a cow-calf-yearling operation, grazing high-desert rangelands and dry forest systems using holistic management.

We have recently published another resource, our second case study in the Rancher-to-Rancher case study series, which showcases approaches ranchers are already using that increase their resilience to a changing climate. This most recent publication describes an operation near Seneca, Oregon, where Jack Southworth runs a cow-calf-yearling operation, grazing high-desert rangelands and dry forest systems using holistic management, with a strong focus on managing for rangeland and soil health. He has implemented a variety of strategies, including some of those described above. These practices, in combination with the ability and willingness to be flexible, have given Southworth’s ranch both ecological and operational resilience. Fundamentally, this allows him to remain profitable now while helping him manage the risks posed by changing climatic conditions.

This article is adapted from a sidebar in the Southworth case study by the same title. The full publication is referenced below, and is available online, with its accompanying video, at


Hall, S.A., Hudson, T.D., Yorgey, G.G., Neibergs, J.S., Reeves, M.C. 2019. Building a Tradition of Adaptive Rangeland Management: Jack Southworth. Rancher-to-Rancher Case Study Series: Increasing Resilience among Ranchers in the Pacific Northwest. Pacific Northwest Extension Publication No. PNW731. Available online at

Leiserowitz, A., Maibach, E., Roser-Renouf, C., and Smith, N. 2011. Global Warming’s Six Americas in May 2011. Yale University and George Mason University.

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New Perspectives at The Tilth Conference

This year CSANR sponsored travel for several WSU students to attend the Tilth Conference in Yakima, WA. We are posting reflections written by the students over the next several weeks. To view student posts from this year and prior years, visit

Daizy Dehnke headshot
WSU student Daizy Dehnke.

My name is Daizy Dehnke, and I’m a sophomore majoring in Organic and sustainable agriculture at WSU. For some important background context, I don’t have any experience regarding agriculture. I’ve helped tend a small garden of peas and potatoes at my family’s home, but I have yet to work for a farm or be part of any agricultural organizations. This has been a newfound interest that has only developed in the last few years of high school. As a result of this, I’m always trying to find ways to immerse myself in the farming culture as much as I can to gain a greater understanding of it beyond theoretical methodology and textbooks.

The Tilth Conference seemed like a great opportunity for me to expand my knowledge of sustainable practices in this way. Not to mention it was located and focused specifically in the Pacific Northwest, which is where I was born, raised, and where I see myself continuing to live after university. Due to registering at the last moment, I had no idea what was in store for me.

Upon arriving at the venue for the first day, I realized I had nothing to be worried about. We were greeted wonderfully with some great breakfast, as well as an introductory ceremony from the Yakama Tribe. Something that was often repeated by many of the other speakers was their awareness of operating on stolen land, which is something I really appreciate. I think it’s important to consider the cultural and historical significance of the land we use, especially as farmers focused on enhancing the quality of life for ourselves, others, as well as the land itself.

Some of my favorite sessions included constructing inexpensive hoop housing, as well as adding renewable energy to the farm. I learned a lot about how to save money by using cheap resources, as well as different kinds of government incentives that provide farmers with funds to add things such as solar panels and more energy-efficient equipment to the farm. These seemed like practical things I wouldn’t necessarily learn from a class but incredibly important in the long run. Additionally, another great thing about these sessions is that those who sat in were very vocal too. Many who attended this conference were sustainable farmers themselves, some of which have been operating for decades. It was always great to hear one jump into the conversation and add in words of advice, or even better alternatives.

While walking around the trading floor, I was able to meet lots of professionals from all sorts of places. One that specifically stuck out to me was Thad Schutt, who created pelletized compost to apply in no-till farms. It was incredibly interesting to be able to talk to him and talk about how he came to create it, as well as the studies around its effects on the soil. I also got to talk to the WSU Everett extension office, the WSDA, as well as several seed companies. It was all incredibly fun and insightful.

All and all, I’m really glad I was able to attend the Tilth Conference and attend the sessions I did. Being around like-minded individuals sharing the same goals and passions was incredibly refreshing, and served as a reminder that there is a promising future ahead of me after university. I’m hoping that I’ll be able to attend more conferences like this in the future!

Understanding Native Tilth

This year CSANR sponsored travel for several WSU students to attend the Tilth Conference in Yakima, WA. We are posting reflections written by the students over the next several weeks. To view student posts from this year and prior years, visit

Tomyia Wallace is a Transfer-Junior at WSU studying Organic and Sustainable Agriculture, originally from Rialto, CA. 

Tomyia Wallace headshot.
WSU student Tomyia Wallace.

When I explained Tilth to my friends and family, I was forced to truly consider what Tilth meant to me and how it compared with the true definition. Tilth in my own definition meant the upkeep and sustainable maintenance of soil. In comparison to the actual definition, Tilth is the condition of tilled soil in respect to the suitability for sowing seeds. While my definition comprises some key components, it is special and tailored to me. Attending the Tilth Conference felt tailored and special in all aspects. Each workshop I attended was unique to the area in which the conference was held and the minorities and under-represented groups that are also a part of the sustainable community. Native Peoples and African Americans were live and present in the Pacific Northwest. The people of Yakama Nation opened the conference with traditional dances that were used to honor the land and the food received. Along with sharing these beautiful dances they taught us some of their history and lineage. In tandem with their history we were privileged to learn about the plants they harvest that are enjoyed during traditional dinners and those used for medicinal purposes. Their passion and drive to maintain traditions displays just how vital sustainability is to native peoples to continue their traditions and ways of living. As a people inhabiting Native Lands it is truly important that we allow those of Native Descent to share their stories while also acknowledging their needs in order to support them in utilizing the land to maintain the lifestyle of their heritage. It was a truly wonderful experience to attend and learn at this year’s Tilth Conference. There were so many workshops I could share about but this one made an impression that will impact my future endeavors in sustainable agriculture.